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Glutamatergic Stimulation of Luteinising Hormone Secretion in Relatively Refractory Male Songbirds
Author(s) -
Deviche P.,
Sabo J.,
Sharp P. J.
Publication year - 2008
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.2008.01771.x
Subject(s) - medicine , endocrinology , sparrow , biology , photostimulation , stimulation , gonadotropin releasing hormone , hypothalamus , glutamate receptor , hormone , luteinizing hormone , zoology , receptor , neuroscience
Seasonal breeding in two Sonoran desert passerines, the Cassin’s ( Aimophila cassinii ) and Rufous‐crowned ( Aimophila ruficeps ) Sparrows is thought to be terminated by the development of a decrease in responsiveness to photostimulation, a condition known as relative photorefractoriness. It was predicted that the development of relative refractoriness is a consequence of a decrease in gonadotrophin‐releasing hormone (GnRH) synthesis and associated stores of releasable GnRH. This hypothesis was tested by determining the luteinising hormone (LH) responses to the excitatory amino acid glutamate agonist N ‐methyl‐ d,l ‐aspartate (NMA) in males of the two species subjected to photomanipulations aimed at generating five groups: Fully photosensitive with undeveloped testes on short days (8L : 16D); fully photosensitive with developed testes on 13L : 11D; relatively photorefractory with regressed testes on 13L : 11D, and groups with developed testes held on 15L : 9D or 16L : 8D. LH release was stimulated in the Cassin’s Sparrow by NMA most in the 8L group; to a lesser, but similar extent in the two 13L groups; and not at all in the 15L and 16L groups. LH release was not stimulated by NMA in any of the photoperiodic regimes in the Rufous‐crowned Sparrow. In both species, NMA induced Fos‐like immunoreactivity in the anterior and basal hypothalamus, but not in GnRH cell bodies. It is concluded that the development of relative photorefractoriness in Cassin’s Sparrows is a consequence of reduced GnRH synthesis, reflected in a reduction in releasable GnRH. The lack of LH response of the Rufous‐crowned Sparrows to NMA administration may be a consequence of high responsiveness to handling stress.